Abstract: An unbalanced bascule bridge having an unbalanced bridge span including a pair of longitudinal girders with a low torsional stiffness interconnected at a pivoting end by a torsionally rigid cross-girder and interconnected along a longitudinal expanse of the longitudinal girders by a steel frame which forms a closely spaced lattice for supporting a relatively thin, lightweight concrete roadway deck. The bascule bridge span is raised and lowered by an actuator assembly including a plurality of hydraulic cylinders pivotally mounted on support columns and corresponding piston rods which apply a torque to the cross-girder through crank-plates welded to the cross-girder and pivotally interconnected to a base. The cross-girder isolates the longitudinal girders from all support and reaction forces while raising and lowering the bascule bridge span.